I wont do it on a dog and I'm a VN...the needle is brutal and if you hit a nerve or vein (especially in a snake as you don't know the detailed anatomy) then you could do some serious damage!
all my javelins are chipped and its massive for the size of snake to be honest, plus with them having such keeled scales it makes it very hard to get it in them
Even the vet who done mine was apprehensive as already mentioned it is tricky and they need to find exactly the right spot. The vet I used had never done a snake and had contacted one of the universities to speak to a reptile expert to find where to place it. Certainly not something to do at home unless you are adequately trained.